1. Field of the Invention
This invention relates to the detection of metallic objects. Specifically, the present invention relates to the detection of metallic objects using an array of imaging giant magnetoresistive sensors.
2. Description of Related Art
Cleanup of unexploded ordnance (UXO) items is a major responsibility for the United States Armed Forces. Such cleanup operations are necessitated as part of the restoration of formerly used defense sites (FUDS) back to civilian use. Given that millions of acres of government property, e.g. FUDS, are contaminated by UXO items, cleanup of FUDS is an expensive undertaking which requires an efficient and accurate solution. As yet another consideration, UXO emplacement is a major problem worldwide. That is, UXO items are responsible for the worldwide death of numerous unsuspecting civilians each year. Thus, UXO detection has substantial utility throughout the United States and the rest of the world.
Many techniques are in use, or have been proposed for use, in UXO detectors. Two of the most commonly employed technologies are electromagnetic induction detection, and fluxgate magnetometry. Time-domain analysis of inductive signals produced by such detection technologies has been suggested as one way to differentiate between hazardous and benign types of buried material. However, neither an induction detector nor a fluxgate magnetometer can be engineered to produce an image of potential UXO objects.
Generating an image of a buried object would tremendously aid in the elimination of false positive UXO detections. False positive UXO detections account for a great part of the expense associated with UXO remediation. That is, prior art detection systems such as pulsed electromagnetic induction systems and cesium-vapor magnetometers are unable to distinguish between UXO and other metallic ground clutter. The inspection of false positives during cleanup of contaminated areas adds greatly to the cost and duration of site remediation. Typically, 50 to 60 pounds of scrap metal are recovered for each ordnance item found using conventional UXO detection technology. An easy-to-use "imaging" UXO detection system would allow a relatively inexperienced user to rapidly distinguish between buried ordnance and other ferrous objects. Hence, an inexperienced user could easily distinguish between, for example, shrapnel or soda cans, or truly dangerous UXO. Thus, the time and expense associated with FUDS remediation could be dramatically reduced by an accurate imaging UXO detection system.
As yet another drawback, prior art UXO detection technologies such as electromagnetic induction and fluxgate magnetometry are not well suited for use in array form as portable UXO detectors. That is, both electromagnetic induction and fluxgate magnetometry sensors are bulky in size and are, therefore, impractical for multi-element portable detector applications.
Furthermore, conventional UXO detection technologies such as the above-mentioned electromagnetic induction and fluxgate magnetometry technologies are ineffective in the presence of a uniform background magnetic field. Hence, such prior art UXO technologies are almost useless for remediation of FUDS situated in strongly magnetic environments. As an example, the Kahoolawe bombing range in Hawaii is located on magnetic volcanic soil. Therefore, prior art UXO detection technologies simply will not work at the Kahoolawe bombing range, or any other strongly magnetic environment.
Although a need exists for an detection system which generates an image of a buried UXO object, a need also exists for a detection system which is well suited to detecting and generating an image of various other metallic objects.
Thus, a need exists for an efficient and accurate unexploded ordnance (UXO) detection system. A further need exists for a UXO detection system which can produce an image of potential UXO objects and eliminate the occurrence of false positive detections. Yet another need exists for a UXO detection technology which can be readily employed in a portable detector. Still another need exists for a UXO detection technology which can function in the presence of magnetic environments such as magnetic soils. A need also exists for an imaging metallic object detector for locating and displaying buried objects other than UXO.